Drilling wells for oil and gas production conventionally employs longitudinally extending sections, or so-called “strings,” of drill pipe to which, at one end, is secured a drill bit of a larger diameter. After a selected portion of the bore hole has been drilled, a string of tubular members of lesser diameter than the bore hole, known as casing, is placed in the bore hole. Subsequently, the annulus between the wall of the bore hole and the outside of the casing is filled with cement before the well is produced. During the drilling of the bore hole, it is often desirable to drill a directional hole, or bore hole, through the side of the casing at an angle to the original bore hole. Such “sidetracking” operations are performed for several reasons, such as avoiding, or drilling around a component that has been previously positioned or become stuck in the casing. In addition, such operations make it possible to drill several so-called “lateral” wells from the original bore hole location.
Many directional drilling techniques include setting an orienting tool such as a whipstock in the bore hole within the casing at a desired depth. A whipstock has an inclined upper face, or ramp, which directs a drilling tool into the sidewall of the casing in the original well bore. Typically, whipstock ramps are comprised of a difficult-to-drill, smooth-surfaced material so as to be more effective in guiding a rotating drilling tool against the casing. Similarly, the casing is typically comprised of a robust, drillable iron-based material such as, for example, a high strength alloy steel. When the whipstock is set in place, a rotating window mill or other drilling tool typically is employed that follows the curve of the whipstock through the casing sidewall. When the rotating drilling tool engages the inner surface of the sidewall of the casing and is essentially wedged between the whipstock ramp and the casing, the drilling tool will often experience a substantial degree of high-amplitude vibration initially as any cutting elements thereon run across and transition between contact with the hard whipstock ramp material and the casing material. These vibrations typically subside once the drilling tool has sufficiently established a cutting pattern in the casing wall. In many cases, this initial, harsh vibration may cause superabrasive cutting elements on the drilling tool to spall or even fracture, and fail prematurely prior to even substantially engaging the casing material and the formation material exterior to the casing.
To enable effective drilling of casing, it would be desirable to have a drill bit or tool offering the capability of protecting the cutting elements upon initially contacting the casing to enable the cutting elements to drill through the casing and subsequent exterior formation material once the casing has been adequately engaged.